Vapor generating plant



NOV- 18, 1947. R. F. lAGl-:R ETAL VAPOR GENERATING PLANT Filed Aug. 22, 1942 INVENToRs Eaymond F lager? BY Car! CHQ/milton ATTORNEY Patented Nov. 18, 1947 VAPOR GENERATING PLANT Raymond F. lager, Fanwood, and Carl C. Hamilton, Plainfield, N. J., assignors to The Babcock & Wilcox Company, Jersey City, N. J., a corporation of New Jersey Application August 22, 1942, serial No. 455,814

6 Claims. l

This invention relates to the construction and operation of vapor generating power installations comprising a vapor generating unit designed to produce superheated vapor under high pressures and high superheat temperatures. Such pressure and temperature requirements complicate the uid circulation system of the unit and necessitate a superheater location close to the furnace chamber where the superheater tubes are subjected to substantial furnace radiation and high temperature gases.

This problem is particularly present in vapor generators of the drumless forced flow type having a flow path for the liquid to be vaporized including one or more long small-bore tubes receiving liquid under pressure at one end and discharging liquid and vapor into a separator at the other end, from which the vapor is passed to a superheater. Vapor generators of this type are particularly designed for high pressure high superheat temperature operation and in view of their ability to economically handle practically instantaneous load changes of a substantial amount are especially suitable for operating conditions such as marine service, where load variations are of a wide range and are required to be met substantially instantaneously.

In installations of the character described, it is usual to supply the steam for the steam driven auxiliaries of the vapor generating unit, such as fuel and water pumps, circulating fans, etc. from the forced circulation vapor generating unit being served. However, the auxiliaries can be driven by steam from other sources, such as a relatively low pressure steam boiler delivering saturated or superheated steam to the auxiliaries. This means that with the high pressure high superheat vapor generator under standby conditions, there will be no steam flow through the superheater of that unit and thus inadequate protection of the superheater tubes from overheating and burning out.

Furthermore, when a vapor generating unit is started up from a cold condition or rapidly changed from a banked condition to a high load condition, the uid in the generating circuits rapidly changes from a high to a low percentage of liquid by volume. This change in liquid volurne causes a surge in liquid level in the vapor and liquid separating chamber which may cause l the superheater to be flooded and slugs of water to enter the high pressure turbine. The surge must be disposed of or the supply of incoming liquid temporarily stopped. If however, the

vapor generator is maintained in a vaporizing condition, the amount of surge on sudden increases in load will be substantially reduced and eliminated as a factor limiting the rate of load change. Operation at a vaporizing minimum load is particularly desirable for forced circula- 2 tion units, as it is preferable from an efficiency standpoint to have all of the fuel burners thereof in operation at all times rather than turning them on or ofi as the load demand changes.

The main object of our invention is the provision of an improved construction and mode of operation of a vapor generating plant of the general character described. A further and more specic object is the provision of an interconnection between a high pressure high superheat vapor generator and a relatively low pressure vapor generator in an installation of the character described which permits continuous operation of the high pressure unit under Vaporizing conditions and consequently a vapor flow through the superheatersection at all times.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specic objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which we have illustrated and described a preferred embodiment of our invention.

The single figure of the drawing is a partly diagrammatic illustration of a portion of a vapor generating power plant incorporating a high pressure high superheat forced circulation steam generator and a relatively low pressure natural circulation steam generator constructed and operating in accordance with our invention.

In the drawing we have diagrammatically illustrated a portion of a two pressure marine power plant constructed and operating in accordance with our invention and embodying a high pressure high superheat forced circulation steam boiler IU and a relatively low pressure natural circulation steam boiler Il. As illustrated, the unit has a middle furnace section I2 fired by fuel burners I 3 in its top wall. The products of combustion are variably divided between upflow gas passes I4 and I5 at opposite sides of the furnace chamber, the pass I4 containing a primary econcmizer section I6 and main steam generating section I1, while the pass I5 contains a tubular air heater I8, a secondary economiser section I9, a primary superheater section 28, and secondary superheatei` section 2|. The gas flow through the gas passes is proportioned by dampers 22 located at the outlet ends thereof. A portion of the steam generating surface is formed by water tubes 23 lining the walls of the furnace chamber and walls below the gas passes I4 and I5 and a convection heated section 24 in the lower part of the gas pass I5 below the second superheater section 2I. The usual auxiliaries, such as the water pump, air blower. and fuel pump for the unit, are preferably driven on a single shaft by an auxiliary steam turbine (not shown). The forced circulation unit described is designed for the production of steam at high pressures and high superheat temperatures, as for example, 1200 p. s. i. temperature requirements necessitate a location for the primary and secondary superheater sections close to the furnace chamber and separated therefrom by only the relatively few rows of convection heated steam generating tubes 24.

The natural circulating steam generating unit illustrated is of the separately red superheater furnace single uptake type disclosed in a copending application of E. J. Rooney, Serial No. 228,734, led September '7, 1938, now U. S. Patent No. 2,332,534, and comprises an upper steam and water drum 30, la laterally offset lower water drum 3 l, a main bank of inclined steam generating tubes 32 connecting the drums 30 `and 3l, a vertical bank of generating tubes 33 extending from the drum 30 Yto a second lower water drum 38 and spaced to enclose a group of steam heating tubes 3d. A main furnace chamber 35 is located between the tube banks 32 and .33 and a separately red auxiliary furnace chamber 36 located at the opposite side of the tube bank 33. A common heating gas outlet V3l' for both furnaces insures passage of the heating gases from the auxiliary furnace over the steam vheating tubes 3d, generating tube banks 33 and32. In theinstallation illustrated the boiler il is designed to produce saturated steam at 415 p. s. i. or superheated steam at '400 p. s. i. and 850F. with a maximum steaming capacity of approximately 54,000 lbs. of steam per hour.

The high and low pressure generating units are designed for complete automatic control. The high pressure steam will be maintained at the desired superheat temperature by control of the gas dampers 22 in the gas passes lll and i5. rEhe temperature of the low pressure steam will be maintained at the desired value by varying the rate of ring inthe auxiliary or superheater fur nace 30 of that unit.

When the high pressure generating unit is operated at its designed rate, the steam generated is passed to the high pressure steam line d incorporating a throttle valve 1i! and leading to a high pressure steam turbine G2 and low pressure turbine V52. When the steam is to be reheated prior to entering the low pressure turbine, the steam heating tubes 34 of the low pressure boiler are used as a reheater and the auxiliaryiurnace red accordingly. The valves d3 and (lll in the steam line 45 are opened and the valve 45 in the saturated steam line 4l to the tubes 3d closed. The valve 4B in the steam discharge line 1li) is opened, the stop valve 50 in the turbine steam line 5l being closed. The reheated steam is then passed to the low pressure turbine 52.

In a two-pressure installation of the character described, the forced circulation unit can be shut down and all of the steam generated by the natural circulation unit. In this case the tubes 34 are used for superheating the saturated steam leaving the drum 30 through the steam line 131. The superheated steam passes through the steam line 139 and control va'lve 55 to the inlet end of the high pressure turbine d2. The valve 55 is closed when the turbines are driven from the high pressure unit.

ln accordance with our invention, the high and low pressure generating units are interconnected by an automatically controlled steam line system in such a manner as to allow a flow of steam and 900 F. The high superheat 4 from the high pressure unit to the low pressure unit and thereby maintain a ow of steam through the super-heater sections 20 and 2l sufcient to protect the same during standby operation and other operating conditions of the high pressure unit. The provisions for this purpose comprise a high pressure steam overflow valve 00 in a branch steam line 6l leading from the high pressure main 40 to the Water drum 3l of the low pressure unit. The line 0l also includes a pressure reducing valve 62 of any suitable type and stop Valves and 64.

The steam overow valve 00 is a daphagm operated valve controlled by an air loaded standardizing relay 05 of the type shown in Gorrie U. S. Patent 2,098,914. The relay 05 is actuated by a pressure responsive device having a Bourdon tube 55a positioning a movable valve member of a pilot valve iib of the type shown in Johnson U. S. Patent 2,054,464 in response to steam pressure Variations in the high pressure main d0. The relay 65 is also actuated by a ilow measuring device 55C through a second pilot valve 651. With this arrangement the relay E55 will be responsive both to steam pressure and steam flow in the high pressure main lill. vThe valve 60 is normally closed and opens automatically under either of two operating conditions of the high pressure unit, i. e. when the steam pressure in the high pressure unit exceeds a predetermined value, the valve will open to relieve the excess boiler pressure, and secondly, whenk the firing rate and thereby the steam 'flow from the high pressure unit falls below a predetermined minimum value. By way of example and not of limitation, in one arrangement of the character described the high pressure unit has a normal generating capacity of 168,000 lbs. of steam per hr. and the valve 60 is arranged to open when the steam flow drops to '16.000 lbs. steam per hr.

When the valve 60 opens, high pressure steam flows from the main d0 through the steam line 0l and valves '60 and 02, the stop valves 63 and 66 being normally open. The reducing valve is set for a pressure reduction to slightly above the operating pressure of the natural circulation unit. The steam line 0! terminates in one or more coils 05 submerged in the water drum 3|. The use of the submerged coil 00 is advantageous to partially desuperheat the steam before emerging into the water. This reduces the noise of the entering steam as well as any tendency t0 torch through the water against the drum shell. n case the natural circulation unit is down .for repairs, the valve 03 is closed and the steam passed into a steam line l0 controlled by a stop valve =ll leading to a desuperheater l2. VThe desuperheated steam passes into Ythe saturated steam main l-l for the generating unit auxiliaries and other saturated steam consuming devices. Likewise the steam entering the water drum 3| is desuperheated Yand passes through the tube bank 32 to the drum 30, from which it can pass to either the saturated steam main 'll or superheater tubes 34 or both, depending upon the load on the installation.

With the described interconnection between the units, the high pressure unit can be maintained in a standby condition or predetermined minimum operating capacity without fear of endangering the superheater thereof. Due to the ow of some Asteam from this unit under such conditions, the amount of surge is greatly reduced on increases in load thereon. Changes in load on the high pressure unit can be more rapidly and reliably effected because the burners thereof can be kept lit at all times, avoiding any necessity of turning burners on or off as the load changes. It is thus possible to maintain a reasonable burning rate or base load and improved efliciency even when the forced circulation unit is idling. The overall eiiiciency of the installation is increased due to the fact that the fuel is burned in only one generating unit most of the operating period. The passage of the steam from the high pressure unit through the natural circulation boiler maintains the low pressure unit in a banked condition without the necessity of having any of the burners thereon lit, reducing the surge in that unit on sudden load increases.

While in accordance with the provisions of the statutes we have illustrated and described herein the best form of the invention now known to us, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of our invention may sometimes be used to advantage without a corresponding use of other features.

We claim:

1. In a vapor generating plant, in combination, a high pressure vapor generator having a vapor superheater positioned in a high temperature Zone, a relatively low pressure Vapor generator, a superheated vapor connection between said superheater and said low pressure generator, a valve arranged to control the iiow of vapor through said vapor connection, and ow and pressure responsive control means connected to said valve and communicating with said vapor connection, said control means being operative to open said valve in response to a rate of superheated vapor ow in said vapor connection less than e, predetermined minimum value and in response to a vapor pressure in said vapor connection above' a predetermined value.

2. In a vapor generating plant, in combination, a high pressure forced circulation vapor generator having a vapor superheater positioned in a high temperature Zone, a relatively low pressure natural circulation vapor generator, a superheated vapor connection between said superheater and said low pressure generator, a valve arranged to control the flow of vapor through said vapor connection, and flow and pressure responsive control means connected to said valve and communicating with said vapor connection, said control means being operative to open said Valve in response to a rate of superheated vapor flow in said vapor connection less than a predetermined minimum value and in response to a vapor pressure in said vapor connection above a predetermined value.

3. In a vapor generating plant, in combination, a high pressure forced circulation vapor generator having a vapor superheater positioned in. a high temperature zone, a relatively low pressure natural circulation vapor generator having an upper liquid and vapor drum, a lower liquid drum, and a bank of vapor generating tubes connecting said drums, a vapor desuperheater tube positioned in and discharging to said lower liquid drum at a point aiding a normal natural circulation in said tube bank, a superheated vapor connection between said superheater and said desuperheater tube, .a valve arranged to control the flow of vapor through said vapor connection, and control means responsive to changes in a variable operating condition in said high pressure generator arranged to automatically operate said valve.

4. In a vapor generating plant comprising a high pressure vapor generator having a vapor superheater positioned in a high temperature Zone in combination with a, relatively low pressure natural circulation vapor generator, the

method of operation which comprises passing superheated vapor from said high pressure generator at a reduced pressure into the liquid space of said low pressure generator whenever the superheated vapor demand on said high pressure generator falls below a predetermined minimum Value and whenever the vapor pressure in said high pressure generator exceeds a predetermined value, and desuperheating the superheated vapor so passed in the liquid space of said low pressure generator before directly mixing with the liquid therein.

5. In a vapor generating plant comprising a high pressure forced circulation vapor generator having a vapor superheater positioned in a high temperature Zone in combination with a relatively low pressure natural circulation vapor generator, the method of maintaining said generators in a standby condition which comprises reducing the firing rate on said high pressure generator, passing superheated vapor from said high pressure generator at a, reduced pressure into the lower part of the liquid space of said low pressure generator at a point aiding a normal natural circulation in said tube bank, discontinuing the iiring of said low pressure generator, and supplying the vapor generated in said low pressure generator by said superheated vapor to the vapor driven auxiliaries of said high pressure generator.

6. In a vapor generating plant comprising a high pressure vapor generator having a vapor superheater positioned in a high temperature zone in combination with a relatively low pressure vapor generator, the method of protecting the superheater during low load periods which comprises passing superheated vapor from the high pressure generator at a reduced pressure into the low pressure generator whenever the vapor pressure in said high pressure generator exceeds a predetermined value and whenever the superheated vapor ows from said high pressure generator drops below a predetermined minimum value.

RAYMOND F. IAGER. CARL C. HAMILTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,709,997 Noack Apr. 23, 1929 226,405 Jurisch et al Apr. 13, 1880 1,959,794 Lucke May 22, 1934 1,711,659 Stender May 7, 1929 1,713,833 Kochendorfer Mav 2l, 1929 2,000,966 Lucke May 14, 1935 2,296,969 Wittmann Sept. 29, 1942 1,897,845 Hilgers Feb. 14, 1933 1,934,723 Lucke Nov. 14, 1933 2,257,805 Kolling Oct. 7, 1941 FOREIGN PATENTS Number Country Date 39,254 Netherlands Sept, 16, 1936 337,245 France Apr. 28, 1938 

